Antenna improvement for 1-wire clock radio aerial? - Canadian TV, Computing and Home Theatre Forums

jpasadena · 2012-05-08, 03:42 PM

Since you brought it up, I had an FM antenna question in another area of the board that was getting the crickets treatment.

Single lead from radio to folded dipole

So here is the question again for the experts in the TV area:

My daughter's Sony clock-radio-CD-player has a single wire coming out the back for an FM antenna. We are in a poor reception area and I can easily build a folded dipole with balun. Question is: how to attach the two leads of the balun to a radio with only one antenna wire?

300ohm · 2012-05-08, 05:38 PM

Quote:

My daughter's Sony clock-radio-CD-player has a single wire coming out the back for an FM antenna. We are in a poor reception area and I can easily build a folded dipole with balun. Question is: how to attach the two leads of the balun to a radio with only one antenna wire?

I also have a similar Sony clock radio (no CD player with it) that has a single wire coming out the back.

Just attach a longer single lead wire to it, and position that wire for the best reception.

stampeder · 2012-05-09, 02:47 AM

Isn't it a case of one side being the chassis ground and the other being the length of wire? Just a guess. If that is so, you could attach one connector from a balun to the chassis/board's ground and the other in lieu of the wire, but I caution about such an oversimplification due to unknown impedance values, etc.

One option might be to have a great FM antenna up on the roof eventually feeding a length of bare conductor equal to the length of the radio's wire, side-by-side with almost no room between them, and then just hope that you get a good re-radiating effect.

holl_ands · 2012-05-09, 02:58 AM

Well, I would drill the back of the case to mount a female 75-ohm coax jack
and then cut back and connect the single wire to the center connector and
find a SIGNAL GROUND to connect to the coax jack's shield/ground tab.
The easiest place might be soldering a short wire to the circuit board's
copper ground plane close to where the single wire antenna connects....or
even better, to a handy component wire where it connects to the ground
plane.

BUT, I'm an experienced Engineer who will double check to make sure that
the manufacturer didn't use a "HOT" chassis (very rare in modern equipment)
with AC ground voltage leakage possibly appearing on the "signal ground",
in which case I would make both connections via [minimum] 1 nF (1000 pf)
capacitors (two each).

Since RF inputs are in the 50-75 ohm range, there shouldn't be any need
for a balun....but I would check the input circuitry just to make sure....

If you don't have experience modifying electronic equipment, find a friend.....

jpasadena · 2012-05-09, 02:52 PM

Thanks for the feedback.

So, holl_ands:
If no balun, then I just strip some RG6 and solder directly onto the folded dipole feedpoint? Seems like heresy after all my experience with DIY TV antennas.

holl_ands · 2012-05-10, 09:31 PM

Clarification: In the mod I described above where I postulated mounting
a female 75-ohm coax connector on the radio's rear panel, a 75-ohm coax would
be run to the location of your FM Antenna (e.g. Folded Dipole or whatever),
which would require a 75-to-300 ohm Balun when connected to the coax cable
since it is a typical 300-ohm impedance antenna.....

stampeder · 2012-05-10, 09:42 PM

On a day when we are reminiscing about Heathkit I just want to add that soldering onto today's tiny circuit boards is quite finicky, so be careful.

2012-05-08, 03:42 PM	#1
jpasadena Rookie Join Date: Jul 2009 Location: Pasadena, CA USA Posts: 21	Antenna improvement for 1-wire clock radio aerial? Since you brought it up, I had an FM antenna question in another area of the board that was getting the crickets treatment. Single lead from radio to folded dipole So here is the question again for the experts in the TV area: My daughter's Sony clock-radio-CD-player has a single wire coming out the back for an FM antenna. We are in a poor reception area and I can easily build a folded dipole with balun. Question is: how to attach the two leads of the balun to a radio with only one antenna wire?

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2012-05-09, 02:47 AM	#3
stampeder OTA Forum Moderator Join Date: Jan 2005 Location: North Delta, BC (96Av x 116St) Posts: 23,338	Isn't it a case of one side being the chassis ground and the other being the length of wire? Just a guess. If that is so, you could attach one connector from a balun to the chassis/board's ground and the other in lieu of the wire, but I caution about such an oversimplification due to unknown impedance values, etc. One option might be to have a great FM antenna up on the roof eventually feeding a length of bare conductor equal to the length of the radio's wire, side-by-side with almost no room between them, and then just hope that you get a good re-radiating effect.

2012-05-09, 02:58 AM	#4
holl_ands Veteran Join Date: Nov 2008 Location: San Diego, CA Posts: 1,635	Well, I would drill the back of the case to mount a female 75-ohm coax jack and then cut back and connect the single wire to the center connector and find a SIGNAL GROUND to connect to the coax jack's shield/ground tab. The easiest place might be soldering a short wire to the circuit board's copper ground plane close to where the single wire antenna connects....or even better, to a handy component wire where it connects to the ground plane. BUT, I'm an experienced Engineer who will double check to make sure that the manufacturer didn't use a "HOT" chassis (very rare in modern equipment) with AC ground voltage leakage possibly appearing on the "signal ground", in which case I would make both connections via [minimum] 1 nF (1000 pf) capacitors (two each). Since RF inputs are in the 50-75 ohm range, there shouldn't be any need for a balun....but I would check the input circuitry just to make sure.... If you don't have experience modifying electronic equipment, find a friend.....

2012-05-09, 02:52 PM	#5
jpasadena Rookie Join Date: Jul 2009 Location: Pasadena, CA USA Posts: 21	Thanks for the feedback. So, holl_ands: If no balun, then I just strip some RG6 and solder directly onto the folded dipole feedpoint? Seems like heresy after all my experience with DIY TV antennas.

2012-05-10, 09:31 PM	#6
holl_ands Veteran Join Date: Nov 2008 Location: San Diego, CA Posts: 1,635	Clarification: In the mod I described above where I postulated mounting a female 75-ohm coax connector on the radio's rear panel, a 75-ohm coax would be run to the location of your FM Antenna (e.g. Folded Dipole or whatever), which would require a 75-to-300 ohm Balun when connected to the coax cable since it is a typical 300-ohm impedance antenna.....

2012-05-10, 09:42 PM	#7
stampeder OTA Forum Moderator Join Date: Jan 2005 Location: North Delta, BC (96Av x 116St) Posts: 23,338	On a day when we are reminiscing about Heathkit I just want to add that soldering onto today's tiny circuit boards is quite finicky, so be careful.